Where does the contamination come from?

Swimming sites can get contaminated from many different sources and therefore pose a health risk to bathers. Some of the more common sources of faecal contaminants are sewage, stormwater, rural run-off and birds.

If you notice any pollution, please contact the Pollution Hotline 24/7 on (03) 366 4663 in Christchurch or 0800 76 55 88 outside of Christchurch.

Sewage

Sewage from many communities is collected via a network of pipes and pumped to a central facility, where it is treated before being discharged to the environment. Sewage consists mostly of water, but also contains organic material and micro-organisms including pathogens. There are a number of factors that can cause sewage to get into the water before it is fully treated. The main ones include:

Broken or leaky pipes - these can be caused by ageing pipes, construction activities or road works. The cost of upgrading much of the country’s ageing pipes to cope with our increasing population is estimated to be several billion dollars. It is anticipated that these upgrades will have to be spread over several decades.

Overflows, during heavy rainfall - If the treatment facility is not able to cope with the large volumes of water entering the sewerage system during heavy rainfall, sewer overflows where sewage gets into the water before it has been treated, can occur. This is made worse where houses have their stormwater drains illegally connected to waste water. Also, some older sewerage systems do not have completely separated sewer and stormwater pipes with stormwater going into the sewerage system.

Emergency overflows - these can also happen periodically during maintenance of sewerage systems.

There are also other sources of sewage:

Properties in areas where there is no sewerage system are typically connected to a septic tank. Where these are older and may have deteriorated, they leak contaminated water into the groundwater system. This contaminated water can end up in a waterway.

Stormwater

Rainwater collected from roofs, driveways, roads, car parks and other sealed surfaces is often piped directly to rivers, lakes and the sea without treatment. During its travels the water (stormwater) collects a number of contaminants along the way. This includes waste from domestic animals, which collects on footpaths, gutters and lawns.

Rural run-off

Farm run-off, can add significantly to the contamination of waterways. Apart from farm oxidation ponds that have been shown to contain high levels of pathogens, a large amount of animal waste ends up on the paddock. Depending on a number of factors – including distance to the nearest stream, rainfall intensity and stock numbers - faecal material ends up in waterways. Where stock has access to streams and rivers for drinking water, excrement may be deposited directly into the water.

Birds

In some water bodies, birds can accumulate in very large numbers because of food supply and breeding needs. Bird faeces can sometimes contain pathogens that can be harmful to humans.